250 CHYMISTRY APPLIED TO AGRICULTURE. 



complete. When all circumstances are favorable, the fer- 

 mentation may be terminated the third day, but it is most 

 commonly prolonged till the fourth or fifth. 



If the operation be well conducted, the fermented liquor 

 will mark only to 1° of the aerometer, {= specific gravity 

 of 1.000 to 1.007;) the more complete the fermentation is, 

 the less will be the specific gravity of the liquor. 



This action should never be violent, as it is well known 

 that in such cases the product is less than when it is slow 

 and regular : whilst it is going on, all the fragments of the 

 potatoes rise to the top and form a crust, which must be 

 separated towards the middle to allow of the escape of the 

 gas. 



In a manufactory where the processes are constantly going 

 on, it is not necessary to form a new ferment for each opera- 

 tion ; about three gallons may be reserved to be made use 

 of when again required. 



Distillation should be so conducted, that the alcohol may 

 pass off equally and regularly, and this can only be done by 

 a judicious management of the fire : the variations of the 

 heat applied to the boiler accelerate or retard distillation, 

 and consequently the alcohol in these two cases is not pro- 

 duced in the same degree : it often happens when the fire is 

 too forcible, that the liquid contained in the boiler is itself 

 forced into the worm of the still. 



It is of importance in a distillery to have an abundance of 

 water, both that the casks may be thoroughly rinsed afler 

 each operation, and for cooling the worm of the still, as with- 

 out this precaution a portion of the alcohol formed would be 

 lost by evaporation. 



By this method four sacks of potatoes yield upon an aver- 

 age 13 gallons and a fraction of brandy, at 20° (= specific 

 gravity of 0.935,) of the aerometer ; if all circumstances 

 are favorable, they may afford 15 gallons. 



When wines are dear and potatoes cheap, the manufac- 

 ture of brandy in this method, is found very profitable : in 

 the year 1816, the advantages arising from it were very great, 

 and even under ordinary circumstances, it may be done with 

 profit. 



The residuum of the distillation, mixed with mustard or 

 turnip cakes, forms excellent food for horned cattle, and is 

 eaten by them with avidity. 



The fecula or starch of potatoes was first converted into 

 a fermentable saccharine substance by M. Kirchoff, of St, 



